Radioactivity detector and discriminator



Feb. 5, 1952 Filed May 12, 1950 S. W. LICHTMAN 2 SHEETS-SHEET 1 IO ll l2 m l4 l5 CATHODE I8 COINCIDENCE DECOUPLING -FoLI OwERa INVERTER -I INVERTER DISCRIMINATOR DIODE F GAMMA AMPLIFIER OUTPUT G.M. TUBE |6 |7 MIXER MIXER DIODE DIODE I 20 2| 22 23 24 CATHODE COINCIDENCE DECOUPLING 553155? 'NVERTER I IscRIMII\I ToR"' DIODE MIXER MIXER DIODE DIODE I 30 3|\ 32\ 33 34 CATHODE COINCIDENCE DECOUPLING -FoLLowERa INVERTER AMPLIFIER DISCRIMINATOR DIO E MIXER MIXER DIODE. DIODE I h l 2\ l/ 3 MIXER MIXER MIXER DIODE DIODE DIODE 41 COINCIDENCE INVERTER INVERTER DISCRIMINATOR COSMIC RAY OUTPUT I INV SAMU EL w. LICHTMAN ENTOR 1952 s. w. LICHTMAN RADIO ACTIVITY DETECTOR AND DISGRIIVII'IIATOR 2 SHEETSSHEET 2 Filed May 12, 1950 ENE-40:24 ON NVENTOR UEL W. LICHTMAN ATTORNEYS Patented Feb. 5, 1952 RADIOACTIVITY DETECTOR AND I DISCRIMINATOR Samuel W. Lichtman, Oxon Hill, Md. Application May-12, 1950, Serial No. 161,676

8. Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) nals produced in a bundle of radiation countertubes exposed to gamma and cosmic radiation.

In cosmic ray studies and in nuclear physics investigations a bundle of closely spaced Geiger- Mueller tubes, connected electrically in parallel relation, is employed to detect cosmic and gamma radiation. Separation of the highly ionizing cosmic radiation from the poorly ionizing gamma radiation is usually predicated upon the ability of the circuits employed to distinguish between single order firing of the tubes caused by gamma radiation and coincident firing of the tubes caused by cosmic radiation. This method of distinguishing cosmic and gamma radiation is well known to the art and the circuits employed generally consists of some form of amplitude discriminatlon, so connected to the counter bundle to distinguish between the large amplitude pulses caused by cosmic radiation and the lower amplitude pulses caused by gamma radiation. Because of the need for maintaining output waveform consistency and critical voltage relationships for amplitude discrimination, the use of amplitude discrimination is often objectionable. This is particularly objectionable where the apparatus must perform continuously over long periods of time with minimum amount of necessary attendance.

The present invention teaches a system. for

separating synchronous and non-synchronous signals originating from a multiplicity of separate signal sources. Also the present invention provides a system wherein the proper operation is not critically dependent upon the wave shape or amplitude of. the exciting pulses.

. It is accordingly an. object of the present invention to provide a new and improved cosmicgamma radiation detection and separation system.

A furtherobject of the present invention is to provide a cosmic-gamma radiation, detection and separation system operable to distinguish between synchronous and non-synchronous firing events. in a multiplicity of radiation counter tubes, I

Another object of. the. present intention. is to provide.- a cosmic-gamma radiation detection and separation system operable independently of the wave shape-or amplitude of the exciting pulses.

Another object. of the present invention is to provide a multiple-channel separator for indi-v eating the presence of synchronous or non-synchronous signals derived from a multiplicity of signal sources.

Another object of the present invention is to provide a multiple-channel signal separator operable to indicate the presence of anoutput appearing from one of the signal sources but inoperable in the presence of an output from more than one signal source.

Still another object of the present invention is to provide a multiple-channel signal separator having appropriate decoupling means for preventing interaction between signal channels.

Other objects and attainments of the present invention will become apparent from the following detailed description when taken in conjunction with the drawings in which:

Fig. 1 is a schematic block diagram of a typi-' cal gated-group discriminator of the present invention, and 1 Fig. 2 is a detailed schematic circuit diagram of the gated-group discriminator shown in Fig. I.

In general and in accordance with the spirit and scope of the present invention a bundle of Geiger tubes is used as previously indicated, to detect highly ionizing cosmic radiation and poorly ionizing gamma radiation. Cosmic radia tion is separated from gamma radiation through the use of a gated-group discriminator which consists primarily of a plurality of signal channels, one for each Geiger tube in the bundle for producing an output indicative of the detection of gamma radiation. Cosmic radiation is indicated, through an additional channel, by coupling all the input signals to a single miXer unit and then to a coincidence discriminator. Finally the present invention teaches a method of and means for, inter-connecting the plurality of channels to prevent an ouput therefrom when a signal is detected by more than one of the' Geiger tubes in the bundle and also teaches a method and means of preventing an output from the cosmic radiation channel when the signal originates from a single tube in the bundle."

For purposes of this application the term gated-group discriminator may be defined as a system wherein the on-off signal switching is dependent upon conduction and non-conduction operation of an electronic tube and wherein the on-off signal switching is furnished by a group of diagram of a gated-group discriminator for separating gamma radiation from cosmic radiation. The system comprises generally a plurality of separating channels, one channel for each Geiger tube employed in the bundle and an additional channel connected to all the Geiger tubes. It is, of course, understood the number of channels shown is merely exemplary and any number of channels may be employed if desired. There is shown in Fig. 1 three Geiger tubes I0, 20 and. 30 and three separating channels associated with the three Geiger tubes.

In operation of the block-schematic diagram shown in Fig. 1, a pulse signal (negative) from any one of the Geiger tubes I0, 20 or 30 is applied to a cathode follower-amplifier ll, 2: or 3| which in turn act as low-impedance .drivers for exciting the various mixer diodes shown in the figure. As will be explained hereinafter, the mixer diodes act to prevent an output from any one channel affecting the output of any other channel. The negative polarity pulse is also inverted in an inverter I2, 22 or 32 and impressed as a positive polarity pulse on an outer grid element of a gated coincidence discriminator tube I3, 23 or 33. Coincidence discriminator tubes I3, 23 and 33 are normally biased to plate current cutoff condition and operate so that a positive polarity signal pulse applied to one of the grid elements is communicated to the output load provided that no signal of negative polarity is present at the same time on a second grid element, as described hereinafter.

The positive polarity pulse impressed on the outer grid element of coincidence discriminators I3, 23 or 33 raises the normally biased to cut-off discriminator to the conducting state. A negative polarity pulse is thereby produced in the anode circuit and passes through a diode decoupler I4, 24 or 34 to common inverter l for all the channels. Diode decouplers I4, 24 and 34 serve to permit paralleling of all output channel pulses on a common line without mutual interaction betweenthe several channels. An output pulse (negative) from any one of the decouplers I4, 24 and 34 is inverted in the single inverter l5 and finally appears as a pulse of positive polarity at the single count (gamma) output terminal l8.

Coincident operation of two or more of the Geiger tubes In, 2|] and 30, upon the detection of cosmic radiation, is prevented from producing an output at terminal |B by the arrangement of the group of diode mixer units associated with each channel. The output from each of the channel cathode followers is connected to the discriminator tube of all the other channels through a separate diode mixer element. This is shown in the block schematic diagram by mixer diodes l6 and H of the first channel tied to the amplifiers 2| and 3| of the second and third channels; mixer diodes 26 and 21 of the second channel tied to the amplifiers II and 3| of the first and third channels; and the mixer diodes 36 and 31 of the third channel tied to the amplifiers H and 2| of the first and second channels. The diode mixer units associated with eac channel are simultaneously tied to what may be called the reject grid of the coincidence discriminators I3, 23 and 33. As described above, the appearance of a negative pulse on a grid of the coincidence discriminator will prevent conduction therein. Since each pair of mixer units are coupled to two amplifiers of the remaining two channels, a negative pulse appearing in any of 7 obtained from the circuits illustrated in the blocks numbered in the 40 series. The signals appearing in any one of the amplifiers ll, 2| or 3| are passed through respective mixer diodes 4|, 42

a and 43 to the grid of inverter 44. This results in the application of a positive polarity pulse on the control grid of coincidence discriminator 45,

. whenever any of the tubes i0, 20 and 30 are fired.

Coincidence discriminator 45 is normally maintained in a non-conducting state, in the same manner as coincidence discriminators I3, 23 and 33 and is rendered conductive with a positive pulse on its control grid in the absence of a negative pulse on its reject grid. Coincident discriminator 45 is'thereby rendered conductive'upon the application of the positive pulse from inverter 44. Conduction in coincidence discriminator 45 produces a negative polarity pulse at its anode which is inverted in inverter 46 and presented as a positive polarity pulse at the coincident (cosmic radiation) output terminal 41.

In the event that more than one Geiger tube is energized at a time, described above, the mixer diodes, l6, l1, etc., and discriminators I3, 23, etc.

would prevent an output pulse from appearing at terminal [8 (gamma output). Normally, however, if only one Geiger tube is energized the coincident channel (cosmic output) would also produce an output as just described. There is incorporated in the present invention additional circuitry to prevent the cosmic channel from rendering an output when the signal is originating from a single channel in order that only cosmic radiation may be indicated at output terminal 41. This is simply achieved by tying the negative polarity pulse that may appear at the input of inverter l5 to the reject grid of cosmic discriminator 45. The presence of the negative polarity pulse on the reject grid of the cosmic discriminator nullifies the effect of any positive polarity pulse applied to the control grid of this discriminator from the mixer units 4|, 42 or 43 thereby preventing conduction therein.

It is seen then that there appears at output terminal l8 a signal that can only have its source from gamma radiation and there appears at output terminal 41 a signal that can only have its source from cosmic radiation. There can be no output on the terminal of one if there is an output at the terminal of the other.

A constructed embodiment of the system just described has a resolving time of 50 microseconds thereby preventing danger of loss of very low cosmic count. For some special applications this resolving time may be reduced by one order of magnitude or more by the use of well known pulse circuit design techniques.

Referring now to Fig. 2 there is shown the circuitry of the gated-group coincidence discriminator as taught in Fig. 1. The vacuum tubes in Fig. 2 carry the same reference numer- A signal arising from point source is applied to the cathode 1o Of grounded grid amplifier II Amplifier I I has its anode 53 tied" to a point. of positive potential 5I through plateresistor I'BI. Grid 69' of amplifier II is grounded at. point. I118 through resistors I05 and F01, and has its cathode HT grounded to point I08 through resistors: I04 and P01. v

The amplified negative polarity pulse appearing at the anode 53 of amplifier II is applied through coupling capacitor 89 to the grid H of inverter tube I2. Inverter I2' is conventional and-has its cathode I2 tied directly to ground at I06 and receives its positive plate potential from source 52 through plate resistor Hi3. In. verter I2 inverts the negative polarity pulse applied to its grid TI to a positive polarity pulse. The positive polarity pulse, takenfrom the anode 54f o1 inverter I2 is impressed on grid element 151 of" coincidence tube l3 through coupling capacitor ,I'II and resistor I12. Coincidence tube I3 is normally biased-to plate current cut-'- 03 by bleeder resistor I 89, and resistance-cw pacitance circuit H2 and H3 tied to cathode T3. Screen grids 14 and 16, tied together, are biased from point of positive potential 52 through voltage reducing resistor II I. Suppressor grid '53 is biased from point of; positive potential 52 and ground through resistors I09 and H3. Anode 55 receives; its voltage from point 52 through plate resistor III). If no signal appears at grid 1"! of coincidence tube I3, 2. negative polarity pulsev is produced at the anode 55 which is applied. through coupling capacitor I21 to the cathode 79 of diode decoupler I4. Diode decouplers. M, 2-4 and 34 are employe in the, circuits to permit the paralleling of all the output channel pulses on a common line without mutual interaction between the discriminator stages and for makin the circuits non-critical. with regard tov selection of the coincidence discriminator tubes. Cathode '!9 of decoupling tube 14 is tied to ground I26 through resistor I24 and the paralleled plates of all the decouple): tubes are grounded at I25 through a common resistor I25. Paralleling; of all the outputchanncls is illustrated here by; decoupling tubes. M}, 24, and 34; each having its cathode con-- nected to. its particular channel discriminator through coupler capacitors I21", E28 and I29 respectively and. the output. from each plate being tied to a common line andfed through coupling capacitor I38 to grid 81 of inverter I5. The. purpos of. tying the outputs of all the channels, together is to having a single output terminal for. the. gamma radiation and to simplify the, circuitry in preventing coincidence tube 45 toconduct on the. occurrence of a single event. Inverter tube [5 is identical in circuit design as inverter tube L2 and serves merely to invert the negative polarity pulse applied to its grid 81 int-0. a. positive polarity pulse. The positive polarity pulse is taken from anode and applied. through coupling capacitor I-6I to terminal I8 to give an indication thereof of the detection of gamma radiation. The outputs I8 and 41, may be connected to any suitable utilization device such as a pulse rate meter or recorder.

In the eventv that the pulse appearing at point source. II] is. not a single pulse but iscoincident with a pulse from one or more of the other counter tubes, there is tied to the output of the amplifier of each channel" a diode mixer for eachadditional; channel, This is shown in Fig. 2 by diode mixers I6 and IT which are respectively tied to the output of the amplifiers-2i and 3I- oi the second and third channels. The output of the amplifiers 2I and 31 (of Fig. 'l). are tied to the cathodesv 82 and 83 through coupling capacitors H5 and I I1. The anodes 59 and 69 of the diode mixers I6 and Il. are tied to a common line so that a signal in any one of the additional channels will appear as a negative pulse at the output. thereof. This negative pulse is applied to grid 77 of coincidence tube '3 through coupling capacitor I I 4 It was above stated that coincidence tube I3 is normally biased to non-conduction and that the appearance of a positive pulse on grid 15 will render it conductive. However, if there also appears a negative pulse on grid 11, as just described, in addition to the positive pulse on grid. 15. coincidence tube I3 will be maintained at its non-conducting state. In this manner there is prevented from appearing an output pulsev at anode 515 of coincidence tube l3 if the signal source is coincident (cosmic radiation) and not a single pulse (gamma radiation).

In order to indicate the highly ionizing cosmic radiation that may be detected in the bundle of Geiger tube detectors, vacuum tubes 4i through 25 form an additional channel operative in conjunction with the plurality of single signal channels. The output signals appearing at the plate of the amplifier in each channel are applied to the cathodes of corresponding mixer tubes 4|, &2 and 53. This is shown in the circuitry of the single channel of Fig. 1 by lead being connected from anode 53 of vacuum II to cathode 8-3 of vacuum tube M through coupling capacitor I32. The output of amplifiers 2I and 3| of the second and third channels are connected to cathodes 85 and 86 of mixer diodes 82 and 43 through coupling capacitors I33 and I35. The cathodes 8 3,85 and 86 of mixer tubes 4|, 42 and 43 are each tied to ground through resistive elements I35, I35 and I 3'5 respectively. The anodes 6|, 62 and 63 are effectively paralleled by being tied to common line H9. There is presented then to grid 9! cf inverter tube id, through common line I16 and coupling capacitor I64, a negative polarity pulse whenever any one or all the input circuits are active.

Inverter t4 merely serves the function of inverting the negative pulse applied to its grid 9| from common line I18 into a positive pulse. The cathode 92 of inverter tube 44 is connected to ground I55 through resistor M9 and grid 9| is connected to ground I55 through resistor 148. The anode 65 of inverter 4% is connected to source of positive potential 52 through plate resistor 42. The positive polarity pulse appearing at anode 66 of inverter 54 is applied, through coupling capacitor I65 and resistor It? to grid SI! of coincidence tube 65.

oincidence tube #5 is operative much in the same manner as coincidence tube I3. Coincidence tube E5 is normally biased to plate current cut-off through capacitance I52 and resistance I53 tied to cathode I60 and ground I 55 and source of positive potential 52- through bleeder resistor I 36. The suppressor grid 95 is also tied to source of positive potential 52 through resistor M5. Anode 68 is tied through resistor I57- to source 52 and combined grids 9t and 53 are tied through voltage reducing resistor IBS, to source 52 and Icy-passed to ground through capacitance i553 These positive grid $6 and 98 functioning as the screengrid for the intermediate grid 91.

inthe event of the applicationto grid 9:! of

a positive pulse from inverter, coincidence tube 45 is raised to its conduction state and there appears a negative pulse at anode 68 which is applied through capacitance l63 to grid 93 of inverter 46. Inverter 46 is operative in exactly the same manner as inverters l2 and I5 and serves to invert the negative pulse impressed on its grid 9| to a positive pulse at its anode circuit 61. The positive pulse is then applied through capacitance I62 to output terminal 41.

An output pulse at terminal 41 is indicative of a coincident firing of at least two of the Geiger tubes in the bundle. If however, a explained above with respect to the block-schematic diagram, there is only a single firing of one Geiger tube there will be prevented from appearing a pulse at the output terminal 41. Although a positive pulse sufficient to render coincidence tube 45 conductive will be applied thereto in the event only a single Geiger tube and its associated channel is active, coincidence tube 45 will be maintained at its non-conductive state by the application of a negative pulse at it reject grid 89. The negative pulse applied to reject grid 99 is obtained from the input to inverter i5 through capacitor I4! and resistor I42. It may be recalled that through the use of mixer tubes I4, 24 and 34 interconnecting the various channels, there can be no pulse at the input of inverter [5 unless it has its source from a single pulse (gamma radiation).

It is seen then, that through the interconnection of the several channels there can only be a pulse output at terminal l8 if its source is from gamma radiation. Also through inter-connecting the common output of the several channels and coincident firing channel there can only be an output at terminal 41 in the event that its source is from cosmic radiation. Thusly it necessarily follow that only one output may be had at a time, an output at one terminal prevents an output at the other terminal.

Although I have shown only certain and specific embodiments of the present invention, it is to be expressly understood that many modifications are possible thereof without departing from the true spirit of the invention.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purpose Without the payment of any royalties thereon or therefor.

What is claimed is:

1. An electrical system for discriminating between synchronous and non-synchronous signals produced by a plurality of distinct signal sources, comprising: a separate signal transmission channel coupled to each signal source to translate signals obtained therefrom, each channel including a circuit responsive to the presence of a signal in any of the other channels for blocking signal transmission through such channel; means combining the outputs from said channels, an auxiliary signal transmission channel coupled to all of said signal sources to translate signals therefrom, including a circuit therein responsive to an output from said combining means to block signal transmission through such auxiliary channel.

2. An electrical system for discriminating between synchronous and non-synchronous signals produced by a plurality of distinct signal sources, comprising a separate signal transmission channel coupled to each signal source to translate signals obtained therefrom, each channel including a circuit responsive to the presence of a signal in any of the other channels forblockingsignal transmission through such channel; means combining the outputs from said channels, an auxiliary signal transmission channel coupled to all of said signal sources to translate signals therefrom, including at least'one vacuum tube having an anode, a cathode and a first and second grid electrode, bias means for maintaining said vacuum tube non-conducting, means for coupling all of said signal sources to the first grid electrode to produce an output pulse at said anode, and means for connecting the output of said combining means to the second grid electrode to block signal transmission through such auxiliary channel. 7

3. An electrical system for discriminating between synchronous and non-synchronous signals produced by a plurality of distinct signal sources, comprising: a separate signal transmission channel coupled to each signal source to translate signals obtained therefrom, each channel .includingat least one vacuum tube havingv an anode, a cathode and at least a first and second grid electrode, bias means for maintaining said vacuum tube non-conducting, means for connecting the signal source to the first grid elec-- trode to produce an output pulse at said anode at the presence of a signal in said channel, circuit means responsive to the presence of a signal in any of the other channels connected to said second grid electrode for blocking signal transmission through such channel, means combining the outputs from said channels, an auxiliary signal transmission channel coupled to all of said signal sources to translate signals therefrom, including a circuit therein responsive to an output from said combining means to block signal transmission through such auxiliary channel.

4. An electrical system for discriminating between synchronous and non-synchronous signals produced by a plurality of distinct signal sources, comprising: a separate signal transmission channel coupled to each signal source to translate signals obtained therefrom, each channel including at least one vacuum tube having an anode, a cathode and at least a first and second grid electrode, bias means for maintaining said vacuum tube non-conducting, means for connecting the signal source to the first grid electrode to produce an output pulse at said anode at the presence of a signal in said channel, circuit means responsive to the presence of a signal in any of the other channels connected to said second grid electrode for blocking signal transmission through such channel, means combining the outputs from said channels, an auxiliary signal transmission channel coupled to all of said signal sources to translate signals therefrom, also including at least one vacuum tube having an anode, a cathode and a first and second grid electrode, bias means for maintaining said last named vacuum tube non-conducting, means for coupling all of said signal sources to the first grid electrode to produce an output pulse at said anode, and means for connecting the output of said combining means to the second grid electrode to block signal transmission through such auxiliary channel.

5. In combination, a plurality of Geiger- Mueller tubes, an electrical system for discriminating between synchronous and non-synchronous signals produced by said tubes, comprising: a separate signal transmission'channel coupled to each Geiger-Mueller tube to translate signals obtained therefrom, each channel including circuit means responsive to the presence of a signal in any of the other channels for blocking signal transmission through such channel, means com-v bining the outputs from said channels, an auxiliary signal transmission channel coupled to all of said signal sources to translate signals therefrom, including a circuit therein responsive to an output from said combining means to block signal transmission through such auxiliary channel.

6. In combination, a plurality of Geiger- Mueller tubes, an electrical system for discrimiode and at least a first and second grid electrode, bias means for maintaining said vacuum tube non-conducting, means for connecting the Geiger-Mueller tube to the first grid electrode to produce an output pulse at said anode at the presence of a signal in said channel, circuit means responsive to the presence of a signal in,

any of the'other channels connected to said second grid electrode for blocking signal transmission through such channel, means combining .the

outputs from said channels, an auxiliary signal transmission channel coupled to all of said Geiger-Mueller tubes to translate signals there-. from, including a circuit therein responsive to an output from said combining means to block signal transmission through such auxiliary channel.

7. In combination, a plurality of Geiger- Mueller tubes, an electrical system for discriminating between synchronous and non-synchronous signals produced by said tubes, comprising: a separate signal transmission channel coupled to each Geiger-Mueller tube to translate signals obtained therefrom, each channel includ-' ing at least one vacuum tube having an anode, a cathode and at least a first and second grid electrode, bias means for maintaining said vacuum tube non-conducting, means for connecting the Geiger-Mueller tube to the first grid, electrode to produce an output pulse at said; anode at the presence of a signal in said channel, circuit means responsive to the presence of a signal in any of the other channels connected to said second grid electrode for blocking signal transmission through such channel, means combining the outputs from said channels, an auX-' iliary signal transmission channel coupled to all of said signal sources to translate signals therefrom, also including at least one vacuum tube having an anode, a cathode and a first and second grid electrode, bias means for maintaining said last named vacuum tube non-conducting, means for coupling all of said signal sources to the first grid electrode to produce an output pulse at said anode, and means for connecting the output of said combining means to the second grid electrode to block signal transmission through such auxiliary channel.

8. In combination, a plurality of radio activity detector tubes, an electrical system for discriminating between synchronous and non-synchronous signals produced by said tubes, comprising: a separate signal transmission channel coupled to each signal source to translate signals obtained therefrom, each channel including a circuit responsive to the presence of a signal in any of the other channels for blocking signal transmission through such channel; means combining the outputs from said channels, an auxiliary signal transmission channel coupled to all of said signal sources to translate signals therefrom, including at least one vacuum tube having an anode, a cathode and a first and second grid electrode, bias means for maintaining said vacuum tube non-conducting, means for coupling all of said signal sources to the first grid electrade to produce an output pulse at said anode, and means for connecting the output of said combining means to the second grid electrode to block signal transmission through such auxiliary channel.

SAMUEL W. LICHTMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,457,790 Wild et al Dec. 28, 1948 2,505,074 Trevor Apr. 25, 1950 OTHER REFERENCES Electron and Nuclear Counters-Korfi, published April 1946 by Van Nostrand Co., Inc., pages 164-171.

Theory and Operation of G-M Counters, Brown Nucleonics, 1948, pages 48-52.

Article Radiation Instruments Using Geiger Muller Tubes, by Weisz, October 1942, Electronics, pages 44 et seq. 

